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The following procedures are involved in the treatment of water for domestic use: (i) What is meant by flocculation? What substance is added to the water to bring it about? (ii) Outline briefly how the filtration of the water is carried out - Leaving Cert Chemistry - Question c - 2007
Question c
The following procedures are involved in the treatment of water for domestic use: (i) What is meant by flocculation? What substance is added to the water to bring i... show full transcript
Worked Solution & Example Answer:The following procedures are involved in the treatment of water for domestic use: (i) What is meant by flocculation? What substance is added to the water to bring it about? (ii) Outline briefly how the filtration of the water is carried out - Leaving Cert Chemistry - Question c - 2007
Step 1
What is meant by flocculation? What substance is added to the water to bring it about?
Answer
Flocculation refers to the process of the coming together or clumping of tiny suspended particles in the water. This process is essential for clarifying water and improving its quality.
The substances commonly added to facilitate flocculation include:
- Aluminium Sulphate [Al₂(SO₄)₃]
- Polyelectrolytes
These agents help to aggregate the tiny particles, making it easier to remove them in subsequent filtration phases.
Step 2
Outline briefly how the filtration of the water is carried out. What is removed from the water by this procedure?
Answer
Filtration is the process of passing water through graded sand or stones to separate out larger particles and impurities.
The key stages of filtration are as follows:
- Water is directed through a filter bed comprising layers of gradated material.
- As the water flows, suspended solids and larger impurities are trapped in the filter material.
- The filtered water then emerges clearer and free of particulates.
This procedure primarily removes:
- Suspended solids
- Debris and Other large impurities
Step 3
If the pH of the water were found to be too low, what substance could be added in order to raise it?
Answer
To raise the pH of water that is found to be too low, a base can be added such as:
- Lime [Ca(OH)₂]
- Calcium Carbonate (CaCO₃)
- A named alkali
These substances help to neutralize acidity by increasing the pH towards a neutral level.
Step 4
How is fluoridation of the water brought about? What is the purpose of fluoridation?
Answer
Fluoridation is achieved by adding fluoride ions to the water supply through various compounds such as:
- Sodium Fluoride (NaF)
- Sodium Hexafluorosilicate (Na₂SiF₆)
- Antimony Hexafluoride (SbF₆)
The primary purpose of fluoridation is to prevent tooth decay, thereby improving public dental health.